Such a shaft coupling is known from EP 0 563 940 A. There, the universal joint is a cross journal pivot joint having a diametrically continuous first joint pin, which is mounted rotatably on a first fork-shaped shaft end, and a centrally interrupted second joint pin, the halves of which are rigidly connected to one another by a tubular intermediate piece and mounted rotatably in a second fork-shaped shaft end. The first joint pin extends with radial play through the tubular intermediate piece between the two halves of the second joint pin, so that the two joint pins are movable relative to one another by a limited angle in relation to the central axis of the universal joint. The pins extend in radial direction away from the central joint axis out beyond their bearing arrangements and there form bearing journals, on each of which one of altogether four anchor blocks is mounted. Formed on each of said anchor blocks on either side of the associated bearing journal is a semicircular moulded piece. Each moulded piece thus associated with the first joint pin is connected to an adjacent moulded piece associated with the second joint body by a flexible coupling element, which has a reinforcing insert embedded in an elastomer and wound around said two moulded pieces. The coupling elements, and hence also their reinforcing inserts, each lie substantially in a tangential plane parallel to the central axis of the universal joint.
When said known shaft coupling has to transmit a torque in one direction, each second one of the altogether four coupling elements is subject to tensile stress; the two associated moulded pieces in said case move in peripheral direction away from one another, with the result that said coupling elements are also subject to bending moments, wherein the individual windings of their reinforcing inserts are loaded very differently and tend to cut into their elastomer covering. The consequence is settling phenomena, as a result of which the force-displacement characteristic of the coupling elements changes relatively quickly and the service life of the coupling elements is limited. In order to achieve a satisfactory service life of the coupling elements, their maximum load has to be kept low, which, given the torque that is to be transmitted via the flexible shaft coupling, is possible only by making the length of the joint pins, and hence the diameter of the shaft coupling as a whole, unusually large. Alternatively or additionally it is necessary for the angular deflections of the two joint pins in relation to one another to be narrowly limited by means of mechanical stops. Such a limitation is achieved in the torsionally flexible shaft coupling known from EP 0 563 940 A by means of the limited play of the continuous joint pin in the tubular intermediate piece of the subdivided second joint pin.
The same applies to other cross journal pivot joints, which are known from U.S. Pat. No. 3,106,076 A or DE 19 28 990 A and likewise have joint pins, which are movable at an angle relative to one another and supported against one another via centrally disposed elastomer bodies. The latter are rapidly destroyed during operation under high torque load.
From DE 42 17 332 A, a tripod joint is known, which comprises a tubular first joint body, which is fastened to a first shaft and has paraxial webs on its inner side, as well as a second joint body in the form of a spider, which is fastened to a second shaft and on each arm of which a roller is mounted rotatably about a radial axis. The rollers run in channel-shaped races, which are inserted in each case between two of the paraxial webs of the first joint body and supported against them by flexible support bodies. These too are incapable of withstanding high torque loads of the joint for a sufficiently long period if they are made of an elastomer that is non-rigid enough to effect adequate vibration isolation.
Front-wheel drives of motor vehicles require shaft couplings that enable large angular deflections of 30 degrees and more and at the same time take up little installation space, above all in radial direction. Said requirements are met by known rigid cross journal joints, tripod joints and cage-controlled constant-velocity pivot joints, which however all have the drawback of virtually undamped transmission of vibrations. In order to eliminate disturbing vibrations, an axial in-line arrangement of such joints and flexible joint discs has therefore been attempted. This leads however to double joint arrangements, in which a torque-transmitting component, e.g. shaft piece, is not adequately guided between the rigid universal joint and the flexible joint disc and may consequently cause an unbalance, which in turn generates disturbing vibrations.